Offset Printing
Most commonly used for forms, letterhead, envelopes, business cards, checks, newspapers, flyers, and books
Offset printing or web offset printing is a commonly used printing technique in which the inked image is transferred (or "offset") from a plate to a rubber blanket, then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water-based film (called "fountain solution"), keeping the non-printing areas ink-free. The modern "web" process feeds a large reel of paper through a large press machine in several parts, typically for several metres, which then prints continuously as the paper is fed through.
4 Head Offset Web Press
The most common kind of offset printing is derived from the photo offset process, which involves using light-sensitive chemicals and photographic techniques to transfer images and type from original materials to printing plates. In current use, original materials may be an actual photographic print and typeset text. However, it is more common — with the prevalence of computers and digital images — that the source material exists only as data in a digital publishing system.
Offset Lithographic printing on to a web (reel) of paper is commonly used for printing of newspapers and magazines for high speed production. In this process, ink is transferred from the ink duct to the paper in several steps:
1) The ink duct roller delivers ink from the ink duct to the ink pyramid, also called the Ink Train.
2) The ductor roller, sometimes called a vibrator roller due to its rapid back and forth motion, transfers ink from the duct roller to the first distribution roller. It is never in contact with both rollers at the same time.
3) The distribution rollers evenly distribute the ink. The first distribution roller picks up the ink from driving rollers, and the last distribution rollers transfer the ink to the form rollers.
4) The transfer rollers transfer ink between the ink-absorbing and ink-delivering driving rollers.
5) Driving rollers roll against the distribution rollers and either absorb or deliver ink, depending on their placement.
6) Ink form rollers transfer ink from the last distribution rollers on to the printing plate.
7) The printing plate transfers the ink to the offset cylinder (typically called the blanket cylinder) usually covered with a rubber "blanket."
8) The paper is then pressed against the blanket cylinder by the impression cylinder, transferring the ink onto the paper to form the printed image.
Sheet-fed refers to individual sheets of paper or rolls being fed into a press via a suction bar that lifts and drops each sheet onto place. A lithographic ("litho" for short) press uses principles of lithography to apply ink to a printing plate, as explained previously. Sheet-fed litho is commonly used for printing of short-run magazines, brochures, letter headings, and general commercial (jobbing) printing. In sheet-fed offset, "the printing is carried out on single sheets of paper as they are fed to the press one at a time." Sheet-fed presses use mechanical registration to relate each sheet to one another to ensure that they are reproduced with the same imagery in the same position on every sheet running through the press.
2 Color Sheetfed Offset Press
Perfecting press: A perfecting press, also known as a duplex press, is one that can print on both sides of the paper at the same time. Web and sheet-fed offset presses are similar in that many of them can also print on both sides of the paper in one pass, making it easier and faster to print duplex.
Web-fed versus sheet-fed
Sheet-fed presses offer several advantages. Because individual sheets are fed through, a large number of sheet sizes and format sizes can be run through the same press. In addition, waste sheets can be used for make-ready (which is the testing process to ensure a quality print run). This allows for lower cost preparation so that good paper is not wasted while setting up the press, for plates and inks. Waste sheets do bring some disadvantages as often there are dust and offset powder particles that transfer on to the blankets and plate cylinders, creating imperfections on the printed sheet. This method produces the highest quality images.
Web-fed presses, on the other hand, are much faster than sheet-fed presses, with speeds in excess of 20,000 cut-offs per hour. (Cut-off is the paper that has been cut off a reel or web on the press. The length of each sheet is equal to the cylinder's circumference.) The speed of web-fed presses makes them ideal for large runs such as newspapers, magazines, and comic books. However, web-fed presses have a fixed cut-off, unlike rotogravure or flexographic presses, which are variable.
Digital Printing
Most commonly used for full color stationary, flyers, signs and brochures.
Digital printing refers to methods of printing from a digital-based image directly to a variety of media. It usually refers to professional printing where small-run jobs from desktop publishing and other digital sources are printed using large-format and/or high-volume laser or inkjet printers. Digital printing has a higher cost per page than more traditional offset printing methods, but this price is usually offset by avoiding the cost of all the technical steps required to make printing plates. It also allows for on-demand printing, short turnaround time, and even a modification of the image (variable data) used for each impression. The savings in labor and the ever-increasing capability of digital presses means that digital printing is reaching the point where it can match or supersede offset printing technology's ability to produce larger print runs of several thousand sheets at a low price.
The greatest difference between digital printing and traditional methods such as lithography, flexography, gravure, or letterpress is that there is no need to replace printing plates in digital printing, whereas in analog printing the plates are repeatedly replaced. This results in quicker turnaround time and lower cost when using digital printing, but typically a loss of some fine-image detail by most commercial digital printing processes. The most popular methods include inkjet or laser printers that deposit pigment or toner onto a wide variety of substrates including paper, photo paper, canvas, glass, metal, marble, and other substances.
In many of the processes, the ink or toner does not permeate the substrate, as does conventional ink, but forms a thin layer on the surface that may be additionally adhered to the substrate by using a fuser fluid with heat process (toner) or UV curing process (ink).
Screen Printing
Most commonly used for apparel or flat promotional products, but may also be used on paper for signs or posters
Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil to receive a desired image. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. A fill blade or squeegee is moved across the screen stencil, forcing or pumping ink through the mesh openings to wet the substrate during the squeegee stroke. Basically, it is the process of using a mesh-based stencil to apply ink onto a substrate, whether it be t-shirts, posters, stickers, vinyl, wood, or other material.
A. Ink. B. Squeegee. C. Image. D. Photo-emulsion. E. Screen. F. Printed image.
Screen printing is also a stencil method of print making in which a design is imposed on a screen of polyester or other fine mesh, with blank areas coated with an impermeable substance. Ink is forced into the mesh openings by the fill blade or squeegee and onto the printing surface during the squeegee stroke. As the screen rebounds away from the substrate the ink remains on the substrate. It is also known as silkscreen, serigraphy, and serigraph printing. One color is printed at a time, so several screens can be used to produce a multicoloured image or design.
Screen printing press
To print multiple copies of the screen design on garments in an efficient manner, amateur and professional printers usually use a screen printing press. Many companies offer simple to sophisticated printing presses. Most of these presses are manual. A few that are industrial-grade-automatic printers require minimal manual labor and increase production significantly.
Screen Printing Press
Flexography
Most commonly used for envelope tint, boxes, brown bags, and plastics.
Flexography (often abbreviated to flexo) is a form of printing process which utilizes a flexible relief plate. It is essentially a modern version of letterpress which can be used for printing on almost any type of substrate, including plastic, metallic films, cellophane, and paper. It is widely used for printing on the non-porous substrates required for various types of food packaging (it is also well suited for printing large areas of solid color).
Flexo has an advantage over lithography in that it can use a wider range of inks, water based rather than oil based inks, and is good at printing on a variety of different materials like plastic, foil, acetate film, brown paper, and other materials used in packaging. Typical products printed using flexography include brown corrugated boxes, flexible packaging including retail and shopping bags, food and hygiene bags and sacks, milk and beverage cartons, flexible plastics, self-adhesive labels, disposable cups and containers, envelopes and wallpaper. In recent years there has also been a move towards laminates, where two or more materials are bonded together to produce new material with different properties than either of the originals. A number of newspapers now eschew the more common offset lithography process in favour of flexo. Flexographic inks, like those used in gravure and unlike those used in lithography, generally have a low viscosity. This enables faster drying and, as a result, faster production, which results in lower costs.
Printing press speeds of up to 600 meters per minute (2000 feet per minute) are achievable now with modern technology high-end printers. Flexo printing is widely used in the converting industry for printing plastic materials for packaging and other end uses. For maximum efficiency, the flexo presses produce large rolls of material that are then slit down to their finished size on slitting machines.
Thermography
Most commonly used for business cards, wedding invitations, greeting cards and other fine stationary.
Thermography is the name of a post print process that is achieved today using traditional printing methods coupled with thermography machines. Thermography machines consist of three sections with a through conveyor.
The first section applies thermographic/embossing powder, made from plastic resins, to the substrate (normally paper). The areas selected for raised printing are printed with slow-drying inks that do not contain dryers or hardeners so that they remain wet during the application of powder. This ink is dried and hardened later during the heating process.
The second section of the process is a vacuum system that removes excess powder from uninked areas of the substrate.
The third section of the process conveys the product through a radiant oven where it is exposed to temperatures of 900 to 1300 degrees Fahrenheit.[2] The heating process takes on the order of 2.5 to 3 seconds. The substrate (usually paper) has a peak in IR absorption at the wavelength used. Through conduction from the paper, the powder temperature rapidly increases and starts melting. When the process is correctly adjusted, the center of the largest filmed areas reach sufficient quality level as the product exits the heater. The melted ink then solidifies as the product cools.
This process is sometimes produced using manual powdering. The substrate with the wet ink is dipped into the powdered polymer. The sheet is then tilted back and forth, rolling the powder across the image. The excess powder is then removed by raising the substrate to a vertical position and lightly tapping the back side. The powdered sheet is then fed into a radiant heating system (as above) at a speed that achieves a good-quality melted film. In the case of craft applications, the powder is melted using a heatgun that blows hot air.
Stationary printed with Thermography
Pad Printing
Most commonly used for promotional products.
Pad printing (also called tampography) is a printing process that can transfer a 2-D image onto a 3-D object. This is accomplished using an indirect offset (gravure) printing process that involves an image being transferred from the cliché via a silicone pad onto a substrate. Pad printing is used for printing on otherwise difficult to print on products in many industries including medical, automotive, promotional, apparel, and electronic objects, as well as appliances, sports equipment and toys. It can also be used to deposit functional materials such as conductive inks, adhesives, dyes and lubricants.
Physical changes within the ink film both on the cliché and on the pad allow it to leave the etched image area in favor of adhering to the pad, and to subsequently release from the pad in favor of adhering to the substrate.
The unique properties of the silicone pad enable it to pick the image up from a flat plane and transfer it to a variety of surfaces, such as flat, cylindrical, spherical, compound angles, textures, concave, or convex surfaces.
Pad Printing Machine
Pad printing cycle
1) From the home position, the sealed ink cup (an inverted cup containing ink) sits over the etched artwork area of the printing plate, covering the image and filling it with ink.
2) The sealed ink cup moves away from the etched artwork area, taking all excess ink and exposing the etched image, which is filled with ink. The top layer of ink becomes tacky as soon as it is exposed to the air; that is how the ink adheres to the transfer pad and later to the substrate.
3) The transfer pad presses down onto the printing plate momentarily. As the pad is compressed, it pushes air outward and causes the ink to lift (transfer) from the etched artwork area onto the pad.
4) As the transfer pad lifts away, the tacky ink film inside the etched artwork area is picked up on the pad. A small amount of ink remains in the printing plate.
5) As the transfer pad moves forward, the ink cup also moves to cover the etched artwork area on the printing plate. The ink cup again fills the etched artwork image on the plate with ink in preparation for the next cycle.
6) The transfer pad compresses down onto the substrate, transferring the ink layer picked up from the printing plate to the substrate surface. Then, it lifts off the substrate and returns to the home position, thus completing one print cycle.
Laser Engraving
Most commonly used for glass, plastics, metal and sturdy fabrics.
Laser engraving, which is different from laser marking, is the practice of using lasers to engrave an object. Laser marking on the other hand just discolors the surface, without cutting into the surface. The technique does not involve the use of inks, nor does it involve tool bits which contact the engraving surface and wear out. These properties distinguish laser engraving from alternative engraving or marking technologies where inks or bit heads have to be replaced regularly.
The impact of laser marking has been more pronounced for specially designed "laserable" materials and also for some paints. These include laser-sensitive polymers and novel metal alloys.
The term laser marking is also used as a generic term covering a broad spectrum of surfacing techniques including printing, hot-branding and laser bonding. The machines for laser engraving and laser marking are the same, so that the two terms are sometimes confused by those without knowledge or experience in the practice.
Dye Sublimation
Most commonly used for apparel and other fabrics.
A dye-sublimation printer (or dye-sub printer) is a computer printer which employs a printing process that uses heat to transfer dye onto materials such as a plastic, card, paper, or fabric. The sublimation name was first applied because the dye was considered to transition between the solid and gas states without going through a liquid stage. This understanding of the process was later shown to be incorrect; since then the process is sometimes known as dye-diffusion, though this has not eliminated the original name. Many consumer and professional dye-sublimation printers are designed and used for producing photographic prints, ID cards, and so on.
These are not to be confused with dye sublimation heat transfer imprinting printers, which use special inks to create transfers designed to be imprinted on textiles, and in which the dyes do indeed sublimate.
Some dye-sublimation printers use CMYO (Cyan Magenta Yellow Overcoating) colors, which differs from the more recognized CMYK colors in that the black is eliminated in favour of a clear overcoating. This overcoating (which has numerous names depending on the manufacturer) is also stored on the ribbon and is effectively a thin layer which protects the print from discoloration from UV light and the air, while also rendering the print water-resistant.
For ID card printing, text and bar codes are necessary, and they are printed by means of an additional black panel on the (YMCKO) ribbon. This extra panel works by thermal transfer printing instead of dye diffusion: a whole layer, instead of just some of the dye in the layer, transfers from the ribbon to the substrate at the pixels defined by the thermal head. This overall process is then sometimes called D2T2 (Dye Diffusion Thermal Transfer).
